1. Field of the Invention
The present invention relates to a broadcast apparatus for a closed space which is used, for instance, in a terrestrial digital broadcast system to retransmit a broadcast signal into a closes space such as a tunnel and an underground mall. More specifically, the invention relates to a technology to accurately and quickly broadcast emergency information such as disaster information and disaster prevention information.
2. Description of the Related Art
In a conventional analog broadcast system, in the case of an occurrence of an emergency situation in a limited space (hereinafter referred to as closed space), since the broadcast system performs an emergency broadcast which broadcasts emergency information only within the closed space, it turns into a grave problem. For example, in the case of an occurrence of an accident in a tunnel, the broadcast system broadcasts the emergency broadcast only within the tunnel. At this moment, the broadcast system displays the emergency information on an electronic bulletin board disposed at this side of the tunnel to alert drivers of vehicles traveling toward the tunnel. However, in such a manner, if the drivers miss out the display, or if the drivers have already passed through the set place of the bulletin board, the drivers do not become aware of the accident in the tunnel at this side of the tunnel and enter the tunnel, never to come to know the accident, and such a situation becomes a cause of a secondary accident.
By the way, specifications of a terrestrial digital broadcast now having come into wide use currently define only first class start (earthquake warning) and second class start (tidal wave warning) as conditions to perform an emergency warning broadcast, because the defined specifications have taken over the specifications of the conventional terrestrial analog broadcast.
On the other hand, in a broadcast field, a technology to broadcast new type of emergency information such as an emergency earthquake prompt report has been developed. However, as matters now stand, the technology which has been under development is still not matched not only to the new type of emergency information but also municipality local disaster prevention information which has been transmitted in the disaster prevention radio system and the emergency broadcast in a closed space.
Now, as for this kind of the emergency broadcast, the Web site of http://www.geocities.co.jp/Technopolis/1549/kinkei.thm# jissi “What is emergency warning system (EWS)?” discloses it in detail.
As mentioned above, although the broadcast apparatus for the closed space has been expected as an accurate and quick notification means for the emergency information, the broadcast apparatus has been in a state that it cannot sufficiently respond to expectations yet.